eighty eight percent nerd.

As I’ve mentioned in past posts, I have augmented the Silverlight Unit Test Framework to log errors it finds into a file in IsoStorage. This file is then read by a python script and results are sent via email if need be.

I ran into a problem today where my python script was throwing an exception on me, stating “Permission Denied” on the result file. I was a little confused, and when I tried to open the file myself [note that this was while my test was still running] I was given the alert:

“The process cannot access the file because it is being used by another process”

Turns out that when you open a file [either by File.Open, or by opening a new IsolatedStorageFileStream] you can set a FileShare flag which will indicate if other processes are allowed to read and/or write to the file at the same time.

private static IsolatedStorageFileStream _resultStream;
private static StreamWriter _resultStreamWriter;

private void OpenResultFile()
{
  // Create an isolated storage file  [make sure to set access to read so that other processes can read this file while it's open for writing].
  IsolatedStorageFile resultStore =
    IsolatedStorageFile.GetUserStoreForApplication();

  // Here I open up my file with ReadWrite access for my test app, and then set Read access for all other processes.
  _resultStream = new IsolatedStorageFileStream("TestResults.txt",
    FileMode.Create, FileAccess.ReadWrite, FileShare.Read,
    resultStore);

  _resultStreamWriter = new StreamWriter(_resultStream);
}

I had been using a different overload of the constructor which did NOT set this flag and so when other processes [namely my python script] was trying to read the file when it was open during the test execution, I would get a permission error.

MSDN – IsolatedStorageFileStream Constructor (String, FileMode, FileAccess, FileShare, IsolatedStorageFile)